Here are 10 facts about Spanish adjectives that will be useful to know as you pursue your language studies:
1. An adjective is a part of speech that is used to modify, describe, limit, qualify or otherwise affect the meaning of a noun, pronoun or a phrase functioning as a noun. The words we most often think of as adjectives are descriptive words — words such as verde (green), feliz (happy), fuerte (strong) and impaciente (impatient).
2. Adjectives in Spanish have gender, and a masculine adjective must be used with a masculine noun, a feminine adjective with a feminine noun following the principle of noun-adjective agreement. Some adjectives change in form with gender, while others don't. Generally, a masculine adjective that ends in -o or -os (in the plural) can become feminine by changing the ending to -a or -as. But singular nouns that don't end in -o generally don't change form to become feminine.
3. Adjectives in Spanish also have number, meaning they can be singular or plural. Again, following the principle of noun-adjective agreement, a singular adjective is used with a singular noun, a plural adjective with a plural noun. Singular adjectives become plural by adding an -s or -es suffix.
4. A very few adjectives are invariable, meaning they don't change form among plural and singular, masculine and feminine. Traditionally, the most common invariable adjectives are macho (male) and hembra (female), as can be seen in the sentence "Los animales macho en general proporcionan muchos menos atenciones parentales que las animales hembra" ("Male animals in general provide much less parental attention than the female animals do"), although you'll also see these words pluralized sometimes as well. Rarely, and then most often in journalese or phrases that have been imported from English, a noun can function as an invariable adjective, as web in the phrase sitios web (websites). Such cases of nouns as adjectives are the exception rather than the rule, and Spanish students should not freely use nouns as adjectives as can be done in English.
5. The default location for descriptive adjectives is after the noun they refer to. When the adjective is placed before the noun, it typically gives an emotional or subjective quality to the adjective. For example, la mujer pobre is likely to refer to a woman who has little money, while la pobre mujer is likely to suggest that the speaker feels sorry for the woman, even though both could be translated as "the poor woman."
6. Most descriptive adjectives can be used as nouns, often by preceding them with a definite article. For example, los felices could mean "the happy people," and los verdes could mean "the green ones."
7. The meaning of some adjectives can be modified by using diminutive or augmentative suffixes. For example, while un coche viejo is simply an old car, un coche viejecito might refer to a quaint car or an older car that someone likes.
8. In sentences of the type "noun is adjective," the adjective might be translated differently depending on whether the verb ser or estar is used. For example, "es seguro" often means "it is safe," while "está seguro" usually means "he or she is certain."
10. A few adjectives are shortened when they appear before singular nouns. One of the most common is grande, which is shortened to gran, as in un gran ejército for "a great army."